In order to define a reference between the sensitivity settings based on notches or side drilled holes and the detectability for near surface cracks under realistic conditions, a number of typical reference reflectors and typical deviations from their ideal orientation have been investigated. The interpretation of the complex reflection on inclined notches has been supported by a theoretical model. This model uses an analytical description of the probe sound field for the reception and the transmission mode, taking into account the elasto-dynamic character of the wave propagation in solid media by simple point directivity functions for longitudinal and shear waves. The pulse shape isdescribed by a quadrupol n model of a piezoelectric transducer element on a perspex wedge. The medium is assumed to be homogeneous and isotropic. The interaction at a crack like defect is taking into account at least 9 possible different sound pathes, among them the classical corner effect, diffraction modes, shear /longitudinal-wave mode conversions direct shear wave reflection e.t.c. The mode conversion at the different surfaces (omposite surface of the plate and crack surface) are taken into account by special point directivity patters for longitudinal and shear waves.
The A-scans are gained by a Fourier transformation. The program works on usual PC's. The present contribution compares different notches with inclinations from 0 to +20°and notches with different depth from 4 to 10 mm. The verification of the model is forthe time being based on two probes: a miniature angle beam probe with 8 x 9 mm²transducer size, 2 MHz frequency and 45° angle of incidence for shear waves. The agreement between the measurements and the theoretical model encourages the use of the clescribed methodology also in other cases, e.g. mode conversion techniques like theLLT-technique as a tandem-replacement approach or for defect characterization and sizing based on a pattern comparison.
Rolf Diederichs 1. Aug 1996, AWS D1.1 ASME B31.1 ASME B31.3 ASME A17.1 ASME Y14.5 AGA XQ0701 XQ0701 ASHRAE 62.1 ashrae 90.1 API 1104 API Std 1104 aashto green book